The invention relates to a submersible compressing station for a well producing gas and oil. The invention has the greatest applicability to offshore oil and gas production, although it may be employed in lakes and bays as well. In such production, wells are drilled from a platform or a semi-submersible vessel, or a drill ship, etc. on the surface of the water into the subsea formations. The well bore is drilled into a petroleum producing formation and the well is completed, i.e. put in condition for producing gas and oil. Many times oil present in a hydrocarbon reservoir contains dissolved gas and the capability of the oil to hold such gas decreases as the pressure decreases and temperature increases.
Once a well is placed in production the raw material flowing from the well may be transported to the surface through a tubing string or riser, or may be transported to the shore through a sub-sea pipeline. Frequently a liquid/gas separator is employed to separate the gas from the oil and water which can be produced by the well. It is often desirable to operate oil and gas production separators at low pressures to improve the well productivity and recovery. When the pressure of the separated gas from the liquid/gas separator is too low to flow to its destination, a gas compressor is usually employed to boost its pressure.
Sub-sea production separators, i.e. separators located on the sea bed, have been used. When sub-sea separators are utilized then the gas compressor must also be located on the sea bed. The disadvantages of mechanical gas compressors include that they often require more power than is practical to supply sub-sea, they have a complex construction, and they are complex to operate and difficult to maintain.
Thus, there has been a need for a reliable sub-sea gas compressor having a robust construction which is simple to maintain and operate. The present invention has the advantages over mechanical gas compressors by utilizing a simple system which consumes less power, and is simpler to operate and maintain.